2-{(E)-[(2Z)-2-(1,2-Di­hydro­phthalazin-1-yl­idene)hydrazinyl­idene]meth­yl}phenol

The title compound, C₁₅H₁₂N₄O, adopts an E conformation with respect to the azomethine bond and crystallizes in its hydrazinyl­idene tautomeric form. The dihedral angle between the ring systems is 15.98 (7)°. The phenol O—H group forms an intra­molecular O—H...N hydrogen bond. In the crystal, pairs of N—H...N and C—H...O hydrogen bonds link neighbouring mol­ecules into centrosymmetric dimers. These dimers are inter­connected by means of three types of π–π stacking inter­actions. One, with a centroid–centroid distance of 3.577 (1) Å [inter­planar separation = 3.4673 (6) Å], connects adjacent mol­ecules into centrosymmetric dimers. The other two inter­actions, on the outward facing sides of the dimers, are between phenol rings of neighboring mol­ecules [centroid–centroid separation = 3.7907 (13) Å and inter­planar separation = 3.5071 (8) Å], and between phthalazin units [centroid–centroid separation = 3.6001 (12) Å and inter­planar separation = 3.4891 (7) Å]. In combination, the π–π inter­actions lead to the formation of infinite layers with mol­ecules stacked along [0-11]. These layers are, in turn, connected with neighbouring layers through the N—H...N and C—H...O hydrogen bonds, yielding a three-dimensional supra­molecular architecture.